Chris Porter, big chief at Mojo Suspension and habitual bike tinkerer, explains his frustrations with the conservatism and convention of the bike industry

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Chris reckons most bike manufacturers are building kids bikes

Chris reckons most bike manufacturers are building kids’ bikes

Why is it so difficult to buy long, low and slack trail bikes?

It’s a question I often find myself asking. And so follows an attempt to find some answers, with apologies to Mondraker, Cesar Rojo and a few quick, enlightened UK journalists. No apologies, however, to the 29er skidders. 😉

Firstly, why is the industry so scared of extreme angles? When Fabien Barel has used head angles of less than 58º (to great success), why do we still think 66º is slack?

bike geo

  • A – Head angle (66º is not slack!)
  • B – Seat angle (steep is actually good!)
  • C – Bottom bracket height (if you’re not dragging your heels, it’s too high)
  • D – Chainstay (short chainstays are great for back hops)
  • E – Front Centre (clue: the front wheel should be in front of you!)
  • F – Wheelbase (currently toying with 1,320mm on the Nicolai)
  • G – Down tube (basically your hands to feet measurement when you stand up to descend)
  • H – Top tube (old-school measurement great for road bikes where you spend all your time sitting down)
  • I – Reach (with stack is a complicated way of telling you the same thing as the down tube)

When you break down the geometry of a bicycle into separate parts it’s actually not that difficult to figure out what’s going on:

If you want to do backhops, get a short rear centre. For anything else you do on an off-road bicycle, you don’t need a short rear centre. If you want to load the front wheel ‘through’ the pedals you’ll need a longer rear centre.

The steeper the head angle, the less you need to lean to achieve a certain cornering arc; great for trials, great for getting round the gates on the canal towpath; not so great for safe, off-road speed.

The higher the BB the more the weight transfer, for better front wheel braking. Changes of direction and manuals are easier too, but a low BB will bring you greater mid-corner stability.

A bigger wheel rolls over bumps better than a smaller wheel… zzzzzzzzzzz. Sorry, sent myself to sleep there with those fairy tales.

“Move any bicycle geometry measurement (that includes wheel diameter) in one direction and it will make something better and something worse”

But here’s the rub. Move any bicycle geometry measurement (that includes wheel diameter) in one direction and it will make something better and something worse, move it in the other and that something will likely get worse as the other thing gets better. Big wheels and steep head angles aren’t good, it’s just that when bike designers first fitted big wheels into frames they simply made the chainstays longer to accommodate them and allow riders to load the front wheel (I use the term designer loosely here). The bars were also accidentally higher which gave more room for the rider, and the contact patch is longer and flatter which quietens the bump and surface camber steer, even with a tiller of a stem. These are all good things… It feels like a ‘normal’ wheeled bike with a decent bar and a slack head angle! Woo hoo!

Ah, that's better!

Ah, that’s better!

But there are bad things too. Just as the larger circumference wheel doesn’t slow down as much on the bump face, so it won’t speed up as much on the back of the bump, rock, root or whatever. No pump, in other words. It’s obviously bigger, but it’s also heavier! So you get a worse sprung to unsprung-weight ratio. Putting that into basic terms, while the wheel goes over the bumps better, the suspension will be much worse. And they accelerate and decelerate more slowly too. Consult your GCSE physics for the details, but put basically, you are adding rotating weight. Incidentally, the low BB in relation to the front axle is also considered a good thing in that it allows the weight on the pedals to push under the front axle at the point of impact, helping to lift the front wheel over the bump. The flip side to that is that when you want to load that front contact patch, those lower feet are also pushing the front wheel on – bad thing for braking.

Because there is less wrap round on the cross-ply tyre carcass to the rim, the tyres roll off the rim more easily. So as 29ers veer from XC to Enduro territory the rims are getting wider and the tyres heavier, and the sprung to unsprung-weight ratio gets worse and the acceleration and deceleration suffers. Oh, and because the hub dimensions didn’t change when the designers got the bigger circle down, there is less spoke angle so the wheel is weaker as well as heavier. Sure 29ers feel OK, even very good in some circumstances, just the small problem of having to drop £2.5K on the carbon wheels to sort them out. You get the feeling they designed themselves into a 29-inch diameter hole and can’t get back out. But they won’t give up, bless ‘em.

“If their riders are struggling with bumps, they consult the suspension experts. They don’t employ a primary school kid to draw a bigger circle”

I use the wheel size analogy because it shows the way most of the bicycle industry develops a theory relating to geometry, or indeed most other design elements. Can you imagine how that would go down with Honda or KTM testing for motocross (which incidentally shares the same outside tyre diameter as a 27.5 x 2.3in or a 26 x 2.8in)? If their riders are struggling with bumps, they consult the suspension experts. They don’t employ a primary school kid to draw a bigger circle. Incidentally, they did try bigger wheels in the 1970s and they tried smaller wheels in the 2000s – tried and failed.

Another nice little illustration of how the industry works is the clutch mech and thick/thin chainring nonsense. When a rear suspension system moves through its arc it requires chain growth – which is accommodated for by the rear mech. So, if we ‘clutch’ that rear mech, we are adding a friction damper to the rear suspension system. Again we make the suspension a bit worse, but this time to keep the chain on? Which it doesn’t fully achieve anyway. That’s hardly a win/win situation, is it? Try a rough downhill run with the chain removed to feel how good the rear suspension can be, and how much faster the bike goes without motive power! Since writing this Neko Mulally did exactly that at the World’s when a mechanical issue turned into his best result ever – watch it for yourself in the video below.

So the development process is more novelty led than performance led. Emperor’s new clothes, anyone?

Maybe it’s because manufacturers build to the lowest common denominator? Maybe they build bikes to feel OK to the slowest, weakest riders? I don’t know, this I’m still trying to work it out for myself. But then I’m someone who rides a trail bike with a 63º head angle! And that’s only because I can’t find a bike I can make even slacker.

So you run a slack head angle on a bike and it works very, very well at speed and is much safer on the steep stuff. The opposite side of the coin is that the bars feel like they flop a bit at low speed, and you need to lean the bike over a bit more to steer when going at low speeds. That’s the sum total of negatives; not many then.

Chris tests all his creatons against the clock. Here the Nicolai gets compared to the Dune XR

Chris tests all his creatons against the clock. Here the Nicolai gets compared to the Dune XR

A bad designer and a lazy bike tester will take these negatives and say it won’t climb. As they ride the slack(ish) bike with no thought to locking their core muscles and taking control of the bike, the bars flop from side to side and the bike gets the blame for the rider’s failings. Neither will that designer/tester get the benefit of the slack head angle, because he or she will probably be too timid to take control of the bike, push it into the turns and feel the handling benefit, and won’t take on very challenging terrain anyway. So this combination of bike designer and tester will end up making canal towpath bikes; bikes built to feel nice at the bars for easy tracks, easy climbs, easy descents.

The only way to understand the effects of geometry changes on handling is to build it and try it, back-to-back, and re-try the original settings to verify the findings. It must all be done with a stopwatch (because it doesn’t lie), with feel as a secondary element (because that does lie).

Add into the mix that the only fast riders trying the stuff that the slow guys are designing (with apologies to Cesar) are a) employed by the companies and probably don’t want to upset them and lose their meal ticket, b) probably happy to ride round problems for a free bike and c) not using stopwatches anyway.

It’s a wonder any company ever releases a genuinely new development in geometry. Still, at least we get sweet, pastel coloured, cartoon graphics – awesome!

Why wouldn’t the slower rider be better off on the best performing, safer geometry and accept the bar flop and the need for a bit of core strength work? Maybe he/she would also be a bit quicker too? Maybe if someone explained that jamming the seat forward in the rails will get you a better climbing angle and saddle/crank relationship, he/she would climb with more comfort too. He/she might even buy a bigger bike (the right size) instead of a longer stem. It seems more important for the industry to hide cables, colour match components and devise ‘standards’ that turn out to be anything but.

Honestly, if MotoGP teams are still learning how to get a bike round corners then it’s way too complicated for the bicycle industry

But while it’s simple in principle, it starts to get really complicated when you try to figure out how to fit all of these geometry elements together to achieve performance over a broad spectrum of circumstances. And I mean really complicated. A 2D drawing of a relatively simple bike that looks great on paper (or a CAD screen), gets massively complicated when you lean it over and ride around a corner. Even more complicated when you add a dynamic rider, who makes up around 80-90% of the vehicle mass, and suspension changing the relationship between the wheels and the chassis too. Honestly, if MotoGP teams are still learning how to get a bike round corners and still improving then it’s way too complicated for the bicycle industry, and certainly too much for me!

Not many people who understand two-wheeled, singletrack, vehicle chassis dynamics actually have jobs in the bicycle industry, and even fewer have the balls to try something ‘different’ when it comes to geometry. Like the fashion industry, everyone wants to copy whatever’s popular, and we end up with the bicycle equivalent of X-Factor; just because something’s popular doesn’t mean it’s good. If you followed this train of thought to its logical conclusion you’d end up with every single manufacturer making heavy, rigid bicycles with 4-inch wide tyres. In all seriousness, that would be stupid wouldn’t it?

Author: Chris Porter

  • The wheels on the cheaper CX were not lighter than the bigger wheels on the FS 29er, which was in itself darned light. Just checked, about the same overall weight, so the wheels were definitely lighter on the FS bike, seeing as the suspension is going to add quite a few grammes to the frame weight.
    Don’t think that pros do not follow fashions and trends or are anywhere near as knowledgeable about bike design as people like Chris who wrote the article. He has plenty of controversial views, but are however usually well thought out.
    Also 29ers are the main option for XC racers in shops, hard to buy anything else.

  • Yeah I am blown away by how fast road riders were this year going up the Death March climb, a super long gravel/dirt road in the Shenandoah mountains. I’m talking guys on 23c tires! Bikes of all sorts can be really versatile, but I’d almost say you results speak more to the big wheels and light weight than the full sus! But do trust what most pros ride, because most ‘pros’ don’t get much of anything in the US, some good discounts if they are lucky. Very very few get top of the line free bikes. So as most all pros are spending their own cash, and virtually all of them are spending it on 29ers, you can’t be assured that 20ers, with low volume tires are faster.

  • But they do believe in sponsors and ride whatever they are given by said sponsors. So I wouldn’t put too much faith in what pros ride. The amount of negative things I’ve heard off the record, both from pro riders and the guys who import and sell bikes with say SRAM kit on them.

    Of note I posted my best Strava time on a rough Roman road DH section on a £5k 29er FS – 1.18 mins, which I think may have been the same model ridden to gold. My second best time on that section later that same day was on a £1.6k cyclocross bike with no suspension and skinny 33c knobs free gravel tyres. How much slower? A whole one second.
    I’d have made up more time than I would have lost on the rare ‘rough’ bits on a CX bike on that London Olympic course. I still wouldn’t be near the top guys though by any stretch of my fevered imagination. I recall watching that race and thinking how much faster it would be on a CX bike.

  • Jesse

    You lost me at saying it’s a “fairytale” that big wheels roll over bumps better. In the 2012 London Olympics 8 of the top 10 were on 29ers, one on a 26er and on 650B. The gold was won on a full sus 29er. Those were the fastest riders on earth, and they don’t believe in fairytales. At least they don’t in XC!

  • AlexXSmith

    I’m a relatively rookie but a 29er Camber was the most amazing ride I’ve ever had….

  • mtbiker045

    I just checked out the Pole bikes (thanks for the links) and I must say VERY interesting design!

  • Dr_Zeek

    one of the (if not, THE) most thought provoking articles I have read about mountain bikes.
    The arguments around wheels size are well documented but the protagonists in the 26, 27.5 and 29er camps have hardly any scientific basis for their arguments.
    I really don’t understand enough about geometry to provide a properly reasoned response but the points made appear to be correct – both intuitively and from riding experience.
    I have often wondered WHY bike shops sell (and riders buy) the latest, greatest (and most expensive) XCM bikes (e.g. spez epic) when such bikes are patently unsuited to the rider’s level of skill and the intended usage.
    I see mates struggling with even moderately technical sections, as they are simply on the WRONG BIKE and the WRONG TYRES.
    Perhaps, if we focused on that riding should be FUN and not impressing our friends or trying to be Platt or Sauser, we’d all be better off – and the bikes would be better too!

  • Eot Lemac

    Thanks Danny. I’ve been pondering fork offset and its relation to rake/trail lately as well. I’d like to try more ‘trail’ by way of reeling in the offset on my fork, but I don’t really have an easy way of doing it. 😉 Currently I’m riding a 951 evo with a dorado.
    Interestingly, back in the day I had a stratos S8 fork which had the offset built into the crowns instead of the dropouts and that fork cornered awesome regardless of the damper settings I used. You could pretty much just lean it into a turn and the back end would let loose…even if you were in the seat. So there may very well be something of value in looking at fork offset.

  • Danny Milner

    Hi Eot,
    Kind of. Nothing concrete, but aside from the obvious ways of getting more front grip, he’s been tinkering with fork offset recently and said it may be something related to this. Your bike may be running a lot of offset, which will affect steering and counter-steering, turn in and front end stability mid corner. He has been experimenting with much shorter offsets – as low as 33mm with 650b – on a 36 fork with the crown and steerer on backwards! He reckons more effort to initiate turn, but locked in grip and acceleration out of corners.

  • Eot Lemac

    Hi Danny, any word from Chris regarding this?

  • Eot Lemac

    Awesome! Thanks Danny.

  • Danny Milner

    Hi Eot
    I’ll forward your question on to Chris and see if he has any suggestions.

  • Eot Lemac

    This article hits the nail on the head and reflects my frustration with the bike industry. For nearly two decades I have been pushing for manufacturers to extend the downtube, slacken the head angle, make adjustable chainstay lengths to accomodate the different front triangle sizes to maintain symmetry….But it usually falls on deaf ears and blank stares….even though I was one of the fastest DH riders on a particular manufacturers team back in the day.

    One of my biggest challenges of late has been getting the newer breed of bikes to corner the way I like – i.e. rear wheel drifting outside of the front WITHOUT dabbing a foot or the rear brake. I’m an experienced rider (professional at one time) and have struggled with the issue of the front letting loose first at limits of traction for a few years now. Perhaps Danny Milner or Chris Porter could chime in on some setup suggestions to get the front end to stick better and the rear to slide sooner?!

  • epakesa

    Chris,

    I think a local bike shop we’ve got here in Jyväskylä, Finland, has built a bunch of bikes you’d love. The new brand is called Pole, and their geometry is pretty impressive: http://www.pole.fi/rinne-yla/#geometry

    In addition to slack head angles, steep seat angles, long chainstays and wheelbases as well as low bottom brackets, they have a very innovative suspension setup that completely eliminates the chain issue you talked about earlier. They call it the Pole link, and in a nutshell it’s a single pivot system where the rear triangle rotates around the bottom bracket – on the same bearings! http://www.pole.fi/rinne-yla/#polelink

    I’d love to hear your thoughts on their bikes since I’m considering buying one for the next season.

  • passtherockplease

    Hi Chris
    As a noobie have found your articles interesting and confusing all the same time

    the whole hate on 29ers is something I just don’t understand, I am faster on my 29er HT on some trails than I am on my old 26inch HT, that said the tigher the turns the more I have to work the 29er and switch backs are just much tougher to go fast( and yes I need lessons) . Easier flowing trails however are much faster on a 29er as you keep more of your momentum.

    The rolling over obstacles thing is better on my 29er than the 26 even on roads with potholes drains etc it feels smoother and I go faster. That said I mainly use my bikes for commuting, I trail ride once a week at most at the moment.

    On the trails, I’d class myself as a beginner, yet I find it easier clipped in than on flats (to be honest I have never ridden flats before this year I have had either toe clips or spd on every bike I have owned) and find that a bigger differentiator than anything geometry wise or wheelsize wise. Seat height tends to be the other thing I notice most especially climbing wise in the saddle where if I am as little as an inch low then I really notice it. Actual size of the frame/geometry comes third for me. I am 5ft10 but have a wingspan and leg length that mean my 29er HT is an XL. but as I am out of the saddle most of the time I find that the difference between XL and L in terms of my reach ( I have tried many) tends to be about an inch which is something my body can accommodate.

    At the moment I am looking at getting FS bike, luckily I have about £3k to spend and I have demoed 29er and 27.5 bikes and I have found the to be very little in it in terms of stability pointing downhill and for some reason a Camber EVO I tried was very plush compared to Giant Trane Advanced 275 0

    In short as a noobie I found 29er HT or FS smoother for me and couldn’t distinguish the subtleties of the head angle. So what am I missing here?

    The reason I am asking is that I am hoping to purchase a FS bike around Christmas time so do I buy a Bike for what my skillset is now or what it could be in the future or is it much of a muchness for a sometime weekend warrior like me.

  • kevinmorice

    So it seems you aren’t a fan of 29’s. And you are in a position to make and sell something that both yourself and the customer (i.e. me) actually want to buy. So why the hell can’t I buy a 26″ anywhere this year?!

  • bressonnemesis

    I understand Chris’ pain but mass market bikes are precisely bike sold to a mass market. I rode a bike with an “edgy” geometry and it was hell on wheels. Beautiful on days when I woke up on the right side of bed. Horrible and awful when my focus and reflexes were “on” that day. Now I’m riding a more conventional bike geometry. Not as much fun but less frustrating.

  • Me

    What stem size do you use Chris?

    What do you think of the Mondraker 10mm stem?